Treatment of zinc carbonate ores



decompose the MgClz .iirstpa'ssed 'through Patented Nov.

UNITED STATES PATENT I o FFICE TR ATMENT or zmc cnitnonnrn onus Niels(J. Christensen, Salt Lake City, Utah Application January 17,1944,Serial No. 518,619 7 13 claims; (CI. 23-61) This invention relates tothe treatmentof zinc carbonate ores which contain relatively largeamounts of calcium and magnesium carbonate and are thereforenotsuited totreatment by acid leaching processes in which the acid consumed in theprocess is not recovered. The process aims to recover the zinc as a highgrade product from such ores and also to recover other metals such asAn, Ag, Cu and Pb, and also'to recover the Ca and-Mg in high gradeproducts, and the C:

as a concentrated gas, and at the same time to regenerate and recoverthe acid consumed in leaching the ore so that it may be reused in thetreatment of more ore.

The process consists in general of five main parts-or steps as outlinedbelow: g I. Leaching the ore with an HClsolution to dissolve the solubleminerals as chlorides and drive oil. the'CQr and precipitatingimpurities from the solution so II. Precipitating the zinc from theZnCle-CaClr-MgCla a hot very concentrated MgClz solution and mixing MgO(recovered in the process) with this solution to form a solid MgClr-MgOproduct.

V, Dryingthe MgCh-MgO prbduct and heating this product with steam andair'(oxy en) to and make MgO and HCl and using the I-ICl again in theleaching operaion.

The complete process 'is illustrated inthe 'accompanying flow sheet andthe-methods of carrying out each step are set forth inthe followingdescription I I Leaching the ore with HCl solution The finelycrus'hedore (a) mi'xed'with wash solution (12) is treated with H01 gases c)-from the decomposing furnace IT in the spray lachers the Ca from thesolution as in the following chemical equations:

rent with the H01 gas (0) and thereafter through spray leaeher 2 incountercurrent to the exit gases (d) from the spray leacher I. By theconcurrent treatment followed by the countercurrent treatment described,the soluble carbonates in the ore are dissolved by direct treatment withthe HCl gases without forming a strongly acid solution and, at the sametime, vnth maximumefliciency in utilization of the H01 gases- In thisleaching process the soluble carbonates are dissolved and the CO: (e) isdriven on as-indicated forming a relatively concentrated chloridesolution.

(Though the method of leaching described above is preferred,the ore maybe leached in any suitable agitator by treatment with an EC] solutionmade by condensing the HCl gases from the decomposing furnace II. Itshould also be noted that the grinding of the oren'iay be either dry orwet. and in the latter case-the grinding may I be carried out in thewash solution (b) to avoid tator on the flow sheet) and, if "themanganese which is dissolved in the leaching operation, the Mn is alsoprecipitated in this land 2, the-mixture of ore and solution beingthe-spray leacher I concur-.

' from the purified addition of excess water in the process.)

' The mixture of chloride solution and ore residue (f) is treated withZnCQ: ore (y) to neutralize the acid; and precipitate the iron fromsolution in the agitator 3 (called Fe-Mn precipiore contains operationby adding chlorine (h) to the solution along with the M003 (or by theaddition of bleaching powder) as indicated in'the following equations: I2Fec1=+sznco3+3mo The ore residue and precipitates (i) are separatedfrom the purified solution (1) and washed with water on the filter 4,the wash solution (1 being used in the leaching operation aspreviouslydescribed. It the tains any valuable metals in solution, such as Ag, Pb,Cd, Cu, etc. these are precipitated by treatment with zinc dust (I) inthe agitator I (indicated as Ag, Pb, Cu, precipitator on the new sheet)and the precipitated metals are separated solution on the filter.

Fe-Mn-free solution (7) contion.

2' 11. Zinc precipitation and recovery k The purified ZnClzCaClz--MgCl:solution (m) from the filterfi, diluted with wash solutions fromsubsequent filtering operations is treated with a chemical equivalent oflime (k) to zinc in solution to precipitate the zinc as ahydroxychloride mixed with magnesium hydroxide as indicated in thefollowing chemical equations:

4ZnC2+3Ca(OI-I)2=2ZI12(OH)3C1+3C&C12 MgClz-l-CMQH) z=Mg (OH) 2+CaCl2 Theprecipitation is carried out in a pebble mill containing small flintpebbles or porcelain marbles, indicated as Zn precipitator 1 on the flowsheet, in order to avoid formation of'lumps and The zine carbonate (s)is separated from the dilute MgC1: solution (t) and washed on the filterl0, the MgClz solution being mixed with the CaClz-MgClgsolution- (o)from the filter 8 and the wash solution (1)) being used to dilute thesolution (m) previous to the zinc precipitation. The zinc carbonate (s)may be dried and marketed as such or may be dried and calcined in thecalciner II to form ZnO and recover the CO: as indicated in thefollowing equation:

the CO2'(r) being usedtocarbonate the mixed precipitates (n) aspreviously described. If the zincus recovered as carbonate thecarbonation is carriedout with CO2 (e) from the leaching opera- III.Precipitation of Ca as baCOa The CaCl-PM'gCh solution from the zincprecipitation, mixed with the MgC1: solution (t) from the carbonationstep and with wash solution (u) from the filter I3 is mixed with finelyground MgO- (121) from the decomposing furnace I? and treated incountercurrent with CO; (e) from the leaching operation in the spraycarbonator I2 (called Ca precipitator'on the fiow sheet) toprecipitatethe calcium as 02100:; as indicated in the following chemicalequation: CaCla+MgO+CO2=CaCO3+MgClz Theprecipitated C'aCOa (w)isseparated from the MgClz solution (It) and washed with water on thefilter l e'the washso'lution (a) being used to dilute the CaCh-MgClzsolution (0) from the "zinc pre. cipitation as previously mentioned. 6

IV. Recovery of a solid MQC'Zz-MQO product ZnCOs ore for recovery offrom the decomposing furnace I1 is mixed with the partially concentratedMgClz solution (yl). The hot concentrated syrupy MgC1: solution (112)from the kiln concentrator l 5 is mixed with sumcient MgO (v3) fromthedecomposing furnace ll to forma solid MgC12MgO product for treatmentin the subsequent decomposing operation. (To avoid loss of HCl in'theconcentrating operation the waste gases from the kiln concentrator maybe sent to the sprayer leacher 2 or to a special scavenging spray fortreatment with the gases.) V. Decomposition of the'MgClz The MgCleMg0product from the pug mill I8 is cushed to approximately six or eightmesh and treated in countercurrent with superheated steam in the muflietype decomposing furnace II to decompose the MgC1: and form MgO and HClas indicated in the following chemical'equation:

the HCl gases (0) being used in the leaching of the zinc carbonate oreas previously described. The decomposition of the MgC1 by the steam is-very rapid and complete at 600 C.-650 C. and

may be carried out with a relatively small excess of steam by passingthe MgC1: product through the furnace in countercurrent to the steam. Atreatment periodof 30-45 minutes by this method is sufiicient to securesubstantially complete decomposition of the MgClz giving a MgO productcontaining only one to two tenths per cent chlorine. The operation maybe carried out in any :suitable type of muilie furnace, such as amultiple hearth, straight line or tower type.

From the foregoing description it will beseen that the process makespossible the treatment of oxidized zinc ores containing relatively largeamounts of CaCO: and MgCOa, due to the fact that the process recoversthe HCl used in the leaching operationfor reuse in theprocess, and

- that the process not only recovers the zinc in a high grade productand (other valuable metals) but, also recovers the calcium and magnesiumin high grade products and the CO2 not used in the manufacture ofproducts in the process in'a pure highly concentrated form.

What is claimed is:

1. The process of treating zinc carbonate ores containing alkali earthcarbonate minerals and magnesium carbonate, which consists in treatingsaid ores with a hydrochloric acid solution to dissolve the zinccarbonate and other soluble carbonates, separating the chloride solutionthus The MgClz solution (it) is evaporated in the I preliminaryconcentrator l4, preferably a multiple efiectevaporator, tosecure arelatively concentrated solution (111) which is further concentrated toform 9, hot very concentrated MgC1: so-

lution (1 2) intheklln concentrator 15. To preventexcessive-decomposition of the MgClz in the kiln concentrator 15 a smallamount of MgO (v2) ;form a, very concentrate ing MgO with said lastconcentrated solution to formed from the treated ore residue, treatingsaid chloride solution with lime and thereby precipitating the zinc as ahydroxychloride together with magnesium hydroxide, separating said mixedprecipitates from the solution, treating said mixed precipitates in anaqueous pulp with C02 and thereby converting the zinc to zinc carbonateand forming MgC1: in solution, separating 5 the zinc carbonate from theMgC1: solution thus formed, treating the solution separated from themixed zinc hydroxychloride magnesium hydroxide precipitate with MgO andC0 and thereby precipitating the calcium therefrom as CaCOa,- separatingthe CaCOa from the MgQlz solution thus formed, evaporating said MgChsolution to MgClz solution, mixiorm a solid MgCl-2MgO product, treatingsaid MgCla-MgO product with steam to decompose the HCl carried in thesethe MgCh and form MgO and HCL and using I-ICl for treating more zincore. &

2. The process of treating zinc carbonate ores containing alkali, earthcarbonate minerals and magnesium carbonate, which consists in leach-Ving said ores with a hydrochloric acid solution to dissolve the zinccarbonate and other soluble carbonates, separating the chloride solutionthus formed from the leached ore residue, treating said chloridesolution with lime and therebyprecipitating the zinc as ahydroxychloride together with magnesium hydroxide, separating said mixedprecipitates irom the solution, treating said mixed precipitates in anaqueous pulp with CO: and thereby converting the zinc to zinc carbonateand forming MgCla in solution, separating the zinc carbonate fromthe-MgClz solutionthus formed, treating the solution separated from themixed zinc hydrochloride-magnesium hydroxide precipitate with MgO and C}and thereby precipitating the calcium therefrom as CaCOs, separating theCaCO: from the -MgCla solution thus formed, evaporating said MgChsolution to form a very concentrated M'gClz solution, mixing MgO withsaid last concentrated solution to form a solid MgCla-MgO prpduct,treating said MgClz-MgQ product with steam to decompose the MgCh andform MgO and HCl, and using said 1101 for leaching more zinc ore andusing said MgO' for precipitatig calcium from more solution asdescribed, and for making a solid MgCla-MgO product from moreconcentrated MgCl-z solution.

3. The process of treating zinc carbonate ores containing alkali earthcarbonate minerals l which consists, in leaching said ores with ahydrochloric acid solution containing MgC'lz to dissolve the zinccarbonate and other soluble carbonates, separating the chloride solutionthus formed from the leached ore residue, treating said chloridesolution with lime in amount substantially chemically equivalent to thezinc in said solution and thereby precipitating the zinc as ahydroxychloride together with magnesium hydroxide, separating said mixedprecipitates 1 from the solution, treating said mixedprecipitates in anaqueous pulp with CO2 and thereby converting the zinc to zinc carbonateand forming MgClz in solution, separating the zinc carbonate from theMgClz solution thus formed, treating the solution separated from themixed zinc hydroxychloride magnesium hydroxide precipitate with MgO andCO: and thereby precipitating the calcium therefrom as CaCOz, separatingthe CaCOz from the MgCh solution thus formed, evaporating said MgClasolution "to form a very concentrated MgCh solution, mixing MgO withsaid last concentrated solution to form a solid MgCla-Mg0 product,treating said MgCl2- MgO product with steam to decompose the MgClz andform MgO and HCl, and using said said 7 and thereby precipitating thezinc as a hydroxychloride together .with magnesium hydroxide,

- separating said mixed precipitates from the solucium therefrom astion, treating said mixed precipitatesin an aqueous pulp with CO: andthereby converting the zinc to zinc carbonate and forming MgCh insolution, separating the zinc carbonate from the MgCl: solution thusformed, treating the solution separated from the 'mixed zinchydroxychloride magnesium hydroxide precipitate with MgO and CO: andthereby precipitating the cal- CaCOa, separating. the CaCO: from theMgCl-z solution thus formed, evaporating said MgCl: solution to form avery concentrated MgCla solution, mixing MgO' with said i lastconcentrated solution to form a solid MgCla- MgO product, treating said'MgCla-IMgO product with steam to decompose the MgCl'z and form MgO andH01, using said HCl for treating more zinc ore and using said MgO forprecipitating calcium from more solution as described. and. for making asolid MgCla-MgO product from more concentrated MgClz solution asdescribed, and calcining said zinc'carbonate to form zinc oxide and C0:and using said CO2 in the precipitation of more zinc carbonate,

5. The process of treating zinc carbonate ores containing iron andmanganese compounds, alkali earth carbonate minerals and magnesiumcarbonate which consists, in treating said ores' with a hydrochloricacidsolution to dissolve the zinc carbonate and other soluble carbonates,

separating the chloride solution thus formed from thetreated oreresidue, precipitating the iron and manganese from said solution withzinc carbonate ore, treating the solution with me-' "tallic zinc toprecipitate metals below zinc in the electromotive series that arepresent in the solution, treating said purified chloride solution withlime and thereby precipitating the zinc as a hydroxychloride togetherwith magnesium hydroxide, separating said mixed precipitates from thesolution, treating said mixed precipitates in -an aqueous pulp with CO2and thereby con- HCl for leaching more zinc ore and using said MgO forprecipitating calcium from more solution as described and for making asolid MgCla- MgO product from more concentrated MgCl2 solution.

4. The process of treating zinc carbonate ores containing alkali earthcarbonate minerals which consists, in treatingsaid ores with a hydro-'chloric acid solution containing MgClz to dissolve the zinc carbonateand.other soluble carbonates, separating the' chloride solution thusformed from the treated ore residue, treating said chloridesolution withlime in amount substantially chemically equivalent to'the zinc in saidsolution verting the zinc to zinc carbonate and forming.

MgClz in solution,'sep arating the zinc carbonate from the MgClzsolution thus formed, treating the solution separated from the, mixedzinc hydroxychloride-magnesium hydroxide precipitate with MgO and COthereby precipitating the calcium therefrom as CaCOs, separating theCaCOa from the MgClz solution thus formed, evaporating said MgClasolution to form a very concentrated MgClz solution, ni'ixing MgO withsaid last concentrated solution to form a solid MgClz- MgO product,treating said MgC1'2MgO prodnot with steam to decompose the MgClz andform metallic zinc to precipitate metals below zinc in the electromotiveseries that are present in the solution, treating said purified chloridesolution with lime and thereby precipitating the zinc as ahydroxychloride together with .magnesillm hydroxide, separating saidmixed precipitates from the solution, treating said mixed precipitatesin an aqueous pulp with CO2 thereby converting the zinc to zinccarbonate and forming MgClz in solution, separating the zinc carbonatefrom the MgClz solution thus formed, treating the solution separated,from the mixed zinc hydroxychloride-magnesium hydroxide precipitatewith MgO and CO: thereby precipitating the calcium therefrom as 09,003,separating the CaCOa from the MgClz solution thus formed, evaporatingsaid MgCl2 solution to form a very concentrated MgCiz solution, mixingMgO with said last concentrated solution to form a solid MgCl2MgOproduct, treating said MgCl2-MgO product with steam to decompose theMgClz and form MgO and HCl, and using said HCl for treating more zincore, using said MgO for precipitating calcium from more solution asdescribed and for making a solid MgCl2MgO product from more concentratedMgC12 solution. I

'7. The process of treating zinc carbonate ores containing iron andmanganese compounds and alkali earth carbonate minerals which .consists,in treating said ores with a hydrochloric acid solution containing MgClzto dissolve the zinc carbonate and other soluble carbonates, separatingthe chloride solution thus formed'from the treated ore residue,precipitating the iron and manganese from said solution with zinccarbonate ore, treating the solution with metallic zinc to precipitatemetals below zinc in the electro'motive series contained in thesolution, treating said purified chloride solution with lime incipitates from the solution, treating said mixed precipitates in anaqueous pulp with CO2 there- 'by converting the zinc to zinc carbonateand forming MgClz in solution, separating the zinc carbonate from theMgCiz solution thus formed,

treating the solution separated from the mixed zinchydroxychlorlde-Inagnesium hydroxide precipitate with MgO and CO2thereby precipitating i the calcium therefrom as CaCOa, separating theCaCOa from the MgClz solution thus formed, evaporating said MgClzsolution to form a very concentrated MgClz solution, mixing MgO withsaid last concentrated solution to form a solid MgCl2-Mg0 product,treating said MgClz-MgO product with steam to decompose the MgClz andform MgOv and HCl, using said HCl for treating more zinc ore, using saidMgO for precipitating calcium from more solution as described and formaking a solid MgCl2MgO product from more concentrated MgClz solution.

8. The process of treating zinc carbonate ores containing other solublecarbonate minerals which consists, in leaching said ores with ahydrochloric acid solution containing MgClz to dissolve the zinccarbonate'and the other soluble carbonates, separating the chloridesolution'thus formed from the leached ore'residue, treating saidchloride solution with lime in amount substantially chemicallyequivalent to the zinc in said solution thereby precipitating the zincas a hydroxychloride together with magnesoium hy-, droxide, separatingsaid mixedprecipitates from the solution, treatingsaid mixedprecipitates in an aqueous pulp with CO2 and thereby converting the zincto zinc carbonate and forming MgClz in solution, separating the zinccarbonate from the-MgClz solution thus formed, treating the solutionseparated from the mixed zinc hydroxychloride-magnesium; hydroxideprecipitate with,

MgO and C02 and thereby precipitating the calcium therefrom as CaCOa,separating the CaCOsfrom the MgClz solution thus formed, evaporatingsaid MgClzsolution to form a very concencining said zinc carbonate toform zinc oxide.

and CO2 and using said CO2 in the precipitation of more zinc carbonate.

9. The process of treating zinc carbonate ores containing other solublecarbonate minerals including magnesium carbonate which consists, inleaching said sores with a hydrochloric acid solution to.dissolve'the'zinc carbonate and other soluble carbonates, separatingthe chloride solu tion thus formed fromthe leached ore residue,

treating said chloride solution with lime in I amount chemicallyequivalent to the zinc in said solution thereby precipitating the zincas a hydroxychloride together with magnesium hydroxide, separating saidmixed precipitates from the solution, treating said mixed'precipitatesinan aqueous prulp with CO2 and thereby converting the zinc to zinccarbonate and forming MgClz in solution, separating the zinc carbonatefrom the MgClz solution thus formed, treating the solution separatedfrom the mixed zinc hydroxychloride-magnesium hydroxide precipitate withMgO and CO2 and thereby precipitating the calcium therefrom a CaCOs,separating the CaCOs I from the MgClz solution thus formed, evaporatingsaid MgClz solution to form a very concentrated MgClz solution, mixingMgO ,with said last concentrated solution to form a solid MgClz- I MgOproduct, treating said MgC1zMgO product with steam todecompose the MgClaand form MgO and HCl, and using said HCl for leaching more zinc ore.

10. The process of treating zinc carbonate ores containing other solublecarbonate minerals in-' cluding magnesium carbonate which'consists, inleaching said ores with a hydrochloric acid solu-" tion to dissolve thezinc carbonate and othersoluble carbonates, separating the chloridesolution thus formed from the leached ore residue, treat ing said'chloride solution with lime in amount chemically equivalent to the zincin solution and thereby precipitating the zinc as a hydroxychlothusformed, treating 'thesolution separated from the mixed zinchydroxychloride-magnesium hydroxide precipitate with Mgo and CO2 therebyprecipitating the calcium therefrom as CaCOa, separating the CaCOs fromthe MgCl-z solution thus formed, evaporating said MgClz solution to forma very concentrated MgCl-i solution, mixing 0 with said lastconcentrated solution to form solid MgClz-MgO product, treating said.MgClz-MgO product with steam to decompose the MgClz and form ,MgO andHCl, using said HCl for leaching more zinc ore, using said MgO forprecipitating calcium irom more solution as ores of zinc anddroxychloride mixed with a 2,303,572' 7 ,h r I described and for makinga. solid MgClz-e-MgO product from more concentrated MECI: solution. 11.A cyclic roess oi treating mixed carbonate magnesium, comprising thesteps of leachiii g the ores with HCl to produce a solu tion ofchlorides, treating said solution of chlorides with lime to form a.precipitate of zinc hymagnesium hydroxide,

treating the precipitate with C02 to'form zinc carbonate, mixingthesolution remaining from said last treatment with the solution remainingfollowing the lime precipitation step, treating said last mixed solutionto precipitate calcium carbotrating the'remaining solution, mixing theconcentrated solution with MgO, treating the mixture thus formed withsteam at a high temperature to produce M80 and HCl, and using the H01 toleach additional quantities of mixed carbonate 12. A process accordingto claim 11,

13. A process according to claim 11, in which a solution of MgCl-a isadded to the leaching solu- NIELS c. CHRISTENSEN.

'nate. separating the calcium-carbonate, concen- V which the ore treatedalso contains calcium car nate.

